1.
If people ~ something such as a plan or an agreement, they decide on it after a great deal of discussion.
The foreign ministers have thrashed out a suitable compromise formula...
= hammer out
PHRASAL VERB: V P n (not pron)
2.
If people ~ a problem or a dispute, they discuss it thoroughly until they reach an agreement.
...a sincere effort by two people to ~ differences about which they have strong feelings.
= hammer out
PHRASAL VERB: V P n (not pron), also V n P